Don't just assume they know what they’re doing. Learn how a recruiter works. Decide if they are a good recruiter to work with or not.
Go beyond the obvious questions questions like 'How long they’ve been a recruiter?' Ask them for lots of details about the job they are seeking to fill. If they know the salary and job title but little else then be cautious. If they don't know much about the job or company besides the most general things then how would they know you are the right person to fill the position? They could end up wasting your time. You don't want a recruiter that is merely emailing or faxing resumes to the client and hoping something sticks.
Besides that sort of recruiter will have little or no influence. The hiring manager will not rely on such a person as a hiring consultant or advisor. As a result they are kept waiting until the employer feels like getting back to them, and then the recruiter has little to tell you besides “they liked you” or “they didn’t like you.”